This invention relates to a flat cathode ray display tube comprising an envelope including a faceplate on which a screen is provided, a partition within the envelope and arranged substantially parallel to, and spaced from, the faceplate, the partition dividing the envelope into a front portion adjoining the faceplate and a rear portion which communicates with the front portion at one end of the envelope, means in the rear portion for producing an electron beam which is directed towards said one end, means in the rear portion for deflecting the electron beam in one dimension, a reversing lens at said one end for deflecting the electron beam into the front portion, and a deflection electrode arrangement carried by the partition and facing the faceplate for deflecting the electron beam in the front portion towards the screen.
A display tube of this kind is described in published British Patent Application No. 2101396A corresponding to U.S. patent application Ser. No. 830,388, filed Feb. 14, 1986 (PHB32794). In this tube the means in the rear portion for deflecting the electron beam in one dimension deflects the beam in a plane substantially parallel to the faceplate in order to effect line scanning, the aforementioned deflection electrode arrangement in the front portion being arranged to deflect the beam in another dimension to achieve frame scanning. Disposed between this deflection electrode arrangement and the screen there is a channel plate electron multiplier which extends parallel to, and is spaced from, the screen. The beam is deflected onto the input side of the multiplier and undergoes electron multiplication within the multiplier, the current multiplied beam emanating from the output of the multiplier being accelerated towards the screen by means of an acceleration electrode on the screen.
In a realised embodiment of this tube, the means for producing the electron beam, namely an electron gun, and the means in the rear portion for deflecting the electron beam are carried on the rear wall of the envelope of the tube which extends opposite the faceplate. The reversing lens comprises a number of parts, a first and second of which are similarly carried on the rear wall of the housing. A further part is carried by the partition, which is in the form of a glass plate. The electrodes of the deflection electrode arrangement are deposited on the surface of this plate facing the screen. The electron multiplier is supported adjacent the screen by a separate member.
It has been found that difficulties can be experienced in manufacturing these tubes repeatedly in a sufficiently dependable manner so far as operational performance is concerned. Moreover the form of construction used does not lend itself to mass production.
It is important to the proper operation of the kind of flat tube described in the opening paragraph that the internal operative components, i.e. the electron beam producing means, deflection means, reversing lens, deflection electrode arrangement, and screen, be positioned and located accurately with respect to one another. It is believed that the problems encountered with the aforementioned tubes may be attributable to the manner of construction employed, with unreliable and insufficient accuracy being achieved in the location of the components with respect to one another.
It is an object of the present invention to provide an improved form of construction of a flat cathode ray display tube of the kind described in the opening paragraph, which lends itself to mass production and as a result of which desired operational performance of the tube can be repeatedly achieved.